1. Field of the Invention
The present invention relates to a tapered coupling structure in which a shaft provided with a taper-shaped outer periphery and a hub provided with a taper-shaped inner periphery are coupled to each other.
2. Description of the Related Art
As a machine element for transmitting the output of a driver to driven equipment, a coupling has been known. Among various types of couplings, there has been known a coupling in which an output shaft of driver provided with a taper-shaped outer periphery in the shaft end portion thereof (hereinafter, referred to as a tapered shaft) and a hub into which the shaft end portion is inserted and which has a hollow part provided with a taper-shaped inner periphery are coupled to each other. This coupling structure is used to transmit high output, for example, to transmit the output of a steam turbine to a compressor, or to transmit engine power to a propeller shaft. In some cases, the hub is provided on the driver side, and the tapered shaft is provided on the driven equipment side.
In the tapered coupling structure (hereinafter, sometimes referred to simply as a coupling structure), when the tapered shaft is coupled to the hub, or when the tapered shaft is decoupled from the hub, oil is fed to the coupling surfaces of the tapered shaft and the hub to increase the diameter of the hub, by which coupling and decoupling are enabled. For this purpose, the coupling structure is configured so that an oil passage is provided in the tapered shaft (or the hub), and an oil groove connecting with the oil passage is provided in the outer peripheral surface of the tapered shaft (or the inner peripheral surface of the hub) to feed oil to the coupling surfaces via the oil passage and oil groove.
Coupling and decoupling of the coupling structure can also be performed by heating and thermally expanding the hub besides the use of hydraulic pressure. However, the work for heating the hub is not easy to perform in the case where the hub is large. Also, the heating of hub may produce thermal deformation of the hub. In this case, it is difficult to reuse the hub as it is as a rotating body.
Therefore, in the coupling structure, coupling and decoupling are performed with hydraulic pressure in most cases.
As described in Japanese Registered Utility Model No. 3054261, the coupling structure in which coupling and decoupling are performed by hydraulic pressure has a problem in that oil scatters from the oil groove, and contaminates the surroundings. Japanese Registered Utility Model No. 3054261 proposes that a fine groove (the depth is 5/100 mm or less) is formed in the inner peripheral surface of the hub. According to Japanese Registered Utility Model No. 3054261, due to the formation of the fine groove, since oil as a complete fluid does not exist on the inner peripheral surface of the hub, even if the tapered shaft is removed and the oil is thereby exposed to the air, the oil does not scatter fluidly and maintains a state of adhering still to the surface layer portion.
The problem of oil scattering can be solved by the proposal of Japanese Registered Utility Model No. 3054261 and further by the kind of oil used. However, with regard to the coupling structure, a problem described below has been brought forward.
To facilitate coupling and decoupling using hydraulic pressure, conventionally, a technique in which an O-ring is interposed between the tapered shaft and the hub has often been adopted. In this technique, a pair of O-rings is disposed at a predetermined interval in the axial direction, and an oil groove is provided between the paired O-rings. By doing this, the oil fed via the oil passage and oil groove is accumulated in a closed space formed by the tapered shaft, the hub, and the paired O-rings, so that a hydraulic pressure for increasing the diameter of hub can be obtained easily.
However, a demand for avoidance of the use of O-rings has arisen. The reason for this is that it is supposed that if the O-ring is broken during the use of the coupling structure, decoupling of the tapered shaft from the hub may become difficult to do.
In the coupling structure without the use of O-rings, the fed oil is liable to leak from the end part of the structure, so that a hydraulic pressure necessary for coupling or decoupling is difficult to obtain. If coupling or decoupling is performed forcedly in this state, scratches occur on the outer peripheral surface of the tapered shaft and the inner peripheral surface of the hub.